Control skylights, control the sun

Q: You wrote an article recently about controlling the light from skylights, and I had never heard of the possibility of doing this. We're lucky to live in a fairly mild climate, but the overheating from the skylights in hot weather makes at least one of our rooms almost unusable. Can you give some more information on what you were talking about?

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By Ken Sheinkopf

southcoasttoday.com

By Ken Sheinkopf

Posted Mar. 15, 2009 at 12:01 AM

By Ken Sheinkopf
Posted Mar. 15, 2009 at 12:01 AM

» Social News

Q: You wrote an article recently about controlling the light from skylights, and I had never heard of the possibility of doing this. We're lucky to live in a fairly mild climate, but the overheating from the skylights in hot weather makes at least one of our rooms almost unusable. Can you give some more information on what you were talking about?

A: Sure. One of the secrets of keeping a home comfortable in the various seasons is to use window controls to block the sun when you don't want it but to let it in when you do. You can do the same with skylights by using products from the skylight manufacturer or other vendors to allow you to control the light coming into your home.

If your home has one or more skylights in it now, you can do a few things to control the sun. For example, you can put a flat or domed glazing across the bottom of the light well. This will help diffuse the light and cut down on its strength coming into the room. You can also buy an operable shade to go under the dome so that you can have the light when you want it but block it partially or even completely when you don't want it. I've seen these advertised by some shade and drapery companies as well as by skylight manufacturers.

If you're planning to have new skylights put into your home, you've got some choices for ones to give you control. You might buy skylights that have a diffusing dome, giving them a milky white appearance.

This type of skylight will diffuse the direct beam of the sun and send the light into the room below it in many different directions. As a result, the light will be softer and more uniform.

You can also buy skylights that have a low solar gain low-e coating that will cut down on heat gain. This doesn't keep sunlight out of the room, but it reflects the invisible infrared portion of the solar radiation which reduces the heat that will get inside.

You should also consider installing a tubular skylight, which is a reflective cylinder or pipe put in between the roof and the ceiling under a clear dome. There's a diffusing glazing across the bottom of the cylinder that keeps the glare-producing rays from getting through.

I've had the skylight blinds from a manufacturer in our home and the minute or so it took to open and close them was well worth the effort, especially during the warmer weather. Buying one of the newer skylights with the features above will eliminate even this minimal effort on your part in many cases.

One warning, though, is to not put window film on skylights, as some people have tried. Yes, this will cut out the direct solar beams, but the film can absorb a lot of the sun's radiation, making it heat up and making the glazing on which the film is attached get pretty hot.

As a result, the glazing material can expand, putting stress on the frame. This is especially troublesome if the glass is part of a two-pane system, and one of the panes gets hotter than the other, with the resulting stress on the mounting system causing one or both of the panes to crack. It can also lead to cracks and even water leakage, so

I suggest you forget about the window film alternative.

Ken Sheinkopf is a communications specialist with the American Solar Energy Society (www.ases.org). Send your energy questions to askken@ases.org.